| With the rapid industrialization and urbanization in the world, soil pollution is intensifying, especially heavy metal contamination, which is unable to meet the demand for land for city development; presence of heavy metals in the sludge restricts the process of using sludge as resources. Soil washing is a fast and efficient technology for removal of heavy metal from soil, and also has great potential for application of sludge heavy metal removal. In this paper, physical enhanced techniques for leaching is studied using a contaminated soil site in Nanjing and sludge form several sewage treatment plant in Nanjing as objects, trying to develop a rapid heavy metal removal technique from contaminated sites and municipal sludge. The main contents and results are as follows:1. A new approach using microwave coupled to EDDS as a leaching agent for removal of Cd, Pb, and Zn from field soils was examined in the laboratory. Effects of time and power of microwave on removal efficiency, fractionation of heavy metals and acute toxicity evaluation after treatment were investigated. The results showed that under microwave condition (900 W* 10 min), the removal efficiencies of Cd, Pb, and Zn were 29%,89%, and 71%, respectively, increased by 8%,26%, and 33%, respectively, compared with those without microwave treatment. In addition, the processing time was greatly reduced from 6 h to 10 min. Sequential extraction results showed that the exchangeable, carbonate bound and Fe-Mn oxide bound fractions of metal concentrations were obviously reduced after treatment, by 34% 90%, and 83% for Cd, Pb, and Zn, respectively, whereas the residual fraction was increased, and mobility and bioavailability of the metal was reduced; according to luminescent bacteria acute toxicity evaluation results, acute toxicity is significantly reduced after microwave-enhanced soil leaching with using EDDS as leaching agent, which reduces ecological risks of heavy metals. Microwave-assisted leaching can be a promising remediation method for heavy metal contaminated sites.2. Leaching traditional conditions was optimized using sludge collected from several sewage treatment plant, and on this basis, physical-enhanced conditions were studied to explore a rapid leaching technique of heavy metals from sludge. And forms of heavy metals and luminescent bacteria toxicity evaluation of treated sludge were investigated to explore the feasibility of ultrasound-enhanced leaching of heavy metals from contaminated sludge.The optimization of the conditions for traditional leaching found that the EDTA and EDDS (3:3) composition was an ideal eluent, water and soil ratio was 30, ethyl lactate (EL) was added of 1%, and the reaction time was 18 h. The conditions were also applicable for the removal of heavy metals in the liquid sludge.The exploration of physical method enhanced sludge washing found that ultrasound did promote leaching process of Zn form contaminated sludge; and there was no need of pre-enrichment process for liquid sludge. The time of the treatment was shortened to 5.5 h.The heavy metal morphology analysis of sludge II showed that, heavy metals in the sludge prior to processing existed in Bl, B2 form, the B2 form of Zn and B2 were transferred to form B1 after treatment by ultrasound-enhanced leaching technology; and luminescent bacteria acute toxicity test showed that luminescent bacteria relative fluorescence intensity of the treated sludge increased significantly, but still had high agricultural sludge potential ecological risk.Through ultrasound-assisted leaching has good application prospects as rapid removal technology of heavy metals from sewage sludge, high coution should be paid on the usage of sludge in agriculture. |
